1. Field of the Invention
This invention relates to wireless data networks and is directed in particular to a procedure for determining a condition of a radio link using radio link control layer observations.
2. Description of the Prior Art
Emerging multimedia digital wireless systems, such as Nortel's UMTS (universal mobile telecommunication system) are designed to support higher data rates than the current narrowband digital networks such as the GSM (global system for mobile) cellular communication system. The architecture of multimedia digital wireless systems is somewhat similar to that of the GSM, in that they are also organized into geographically-defined cells, with a base transceiver station (BTS) that controls operation of all mobile radio terminals present in the area covered by the BTS. BTS (also called “Node-B”) hosts radio transmission/reception equipment for operating a number of radio channels, maintains authorization and registration of the mobile terminals, handles channel allocations for all active communication sessions, etc.
Typically, a group of base transceiver stations communicate with one or more radio network controllers RNC located throughout a certain territory. A RNC is analogous with what is referred to as a Base Station Controller (BSC) in GSM. Each radio network controller is responsible with controlling operation of the base transceiver stations coupled to it, and hosts for example the radio equipment for a public line mobile network (PLMN), transcoder units (TCU) and portable communication units (PCU). A RNC is in turn coupled to a mobile gateway mobile switching center, which performs switching operations for both circuit-switched and/or packet-switched communications.
Layered architecture is a form of hierarchical modularity used in data network design, where each layer performs a category of functions or services using information from the immediately upper or lower layers. The OSI (Open System Interconnections) model defines a Physical Layer (Layer 1), a Data Link Layer (Layer 2), a Network Layer (Layer 3), a Transport Layer (Layer 4) and one or more Application Layers (Layers 5 to 7).
The Physical Layer (L-1) specifies the standards for the transmission medium, which is a radio (wireless) link in case of wireless networks. A wireless link is characterized by a higher bit error rate than a wired link, due to RF environment such as fading and effects of interference etc, and low transmission power available to the mobile terminal. In addition, the radio link is not symmetrical and the bandwidth of a transmission channel rapidly fluctuates over time. Furthermore, in a wireless environment, the amount of bandwidth available is fixed and scarce. Adding bandwidth to a radio link may be expensive or even impossible due to regulatory constraints. Still further, part of the bandwidth needs to be used in signalling and error correction, which reduce the bandwidth allocated to the payload.
Data Link Layer (L2), which is called the Radio Link Control (RLC) layer for wireless data networks, performs control protocols used to mitigate the effects of impairments introduced by the physical transmission medium. In the case of a wireless network, the RLC protocols are designed to deal specifically with the types of impairments found on the radio link and comprise mechanisms to deal with errors on the link, delays encountered in transmitting information, lost information, bandwidth conservation, and contention resolution.
Layers 3–7 are less relevant to the present invention and as such are not discussed further.
Since the main limitation in the wireless systems is the scarcity of the radio resources (power and spectrum), one of the main objective when designing a wireless system is to best utilize the available resources. Various radio resource management (RRM) algorithms have been designed with a view to maximize the capacity and performance of a wireless system, while efficiently using the available radio resource.
Due to the nature of the RRM (radio resource management) functions, most RRM algorithms are implemented at L-2 or above, and usually reside in the RNC (Radio Network Controller). However, for a RRM algorithm to function properly, it is essential that it has the states of the L-1 radio link as the input information; this information is available at the BTS (Base Transceiver Station) and at the mobile terminal. Since in most wireless systems the RNC and the BTS are not co-located, this architecture results in using an important chunk of the available bandwidth for signalling exchanges between these two entities as well as signalling exchanges between RNC and mobile terminal. For example, for wireless data services, radio rate link adaptation schemes are mandatory. The conventional implementation of link adaptation is to use explicit signalling; this occupies link bandwidth within both the air interface and the lub/backhaul (NodeB/BTS-RNC/BSC interface), as well as adds complexity into the system.
There is a need to reduce the signalling between the user equipment, the BTS, and the RNC, that is necessary for providing the RNC with L-1 operational parameters of the radio link.